This invention relates to machine tools and more particularly to an anti-whip device for a drive screw of a machine tool used to displace one component relative to another component of the machine.
In a particular type of machine tool in the prior art, there is provided a base member, a workpiece support table mounted on the base member, a gantry member supported on the base member and adapted to be displaced relative to the base member along a longitudinal line of travel commonly referred to as the y-axis, a toolhead support assembly mounted on the gantry member and adapted to be displaced relative to the gantry along a transverse line of travel commonly referred to as the x-axis, and a toolhead assembly having one or more tools mounted thereon and engageable with a workpiece positioned on the worktable, mounted on the toolhead support assembly and adapted to be displaced along a vertical line of travel commonly referred to as the z-axis.
Typically, the gantry member is supported on a pair of guideways rigidly secured to the base member, and is displaceable along the y-axis by a pair of elongated drive screws mounted on the sides of the base member, operatively connected to the gantry member. Each of such drive screws is supported at its ends on bearings mounted in brackets secured to the base member, is driven by a motor mounted on the base member and operatively connected to an end portion of the drive screw and further is provided with a follower assembly secured to the gantry member and operatively connected to the drive screw so that upon operation of the drive motor to rotate the drive screw, the interaction between the drive screw and the follower assembly will cause the gantry member to be displaced along the y-axis.
Because such elongated drive screws are supported only at their ends, the middle portions thereof tend to sag, creating an out of balance condition when the drive screws are rotated, particularly at high speeds. As the drive screw is driven at higher speeds, the center thereof characteristically begins to rotate in larger and larger circles until a critical speed at which point the drive screw vibrates violently, a condition which adversely affects the operation and longevity of the machine and which is sought to be avoided.
The problem presented by such operating condition of drive screws of machines of the type described has to a large extent obviated by the use of supports for the mid-portions of such drive screws as provided in U.S. Pat. No. 5,425,607. In the anti-whip device disclosed in such patent, the device supporting the mid-portion of a drive screw operated to displaced the gantry member along the Y-axis is adapted to be cammed out of the path of the leg section of the gantry member operatively connected to the drive screw. It has been found, however, that although the anti-whip device provided for in such patent is highly effective in supporting the mid-portion of the drive screw, thus preventing a whipping action of the screw, it is not entirely effective in supporting the drive screw and is fairly costly to manufacture and install. It thus has been found to be desirable to provide an anti-whip device operable to support the mid-portion of a drive screw of a machine of the type described, which is as effective as the anti-whip device of the aforementioned patent but less costly to manufacture and install.
In providing an improvement over prior art devices for supporting the mid-portions of drive screws in a machine of the type described, the present invention provides for a drive screw support member supported on the base member of the machine for pivotal movement about a transverse axis, having angularly spaced arm sections alternatively disposable in a line of travel of the operating connection of the gantry to the drive screw and engageable with the drive screw in supporting relation at a point intermediate the ends thereof, each such arm sections being engageable by a component of the gantry member as it traverses along the drive screw to cause such arm section to be engaged and pivoted out of its drive screw support engagement, ahead of such operative connection and simultaneously cause the other of such arm sections to pivot into its drive screw support engagement, behind the passage of the operative connection between the gantry and the drive screw. Biasing means in the form a of spring interconnecting the base member of the machine and the drive screw support member, alternatively yieldingly biases the arm sections of the support member into support engagement with the mid-section of the drive screw.